Difference between clearing cache in internal memory and removable memory in android

I know that we can cache files in android

• Internal memory (phone memory)
• Removable memory (SD-CARD)

So, I know that android does housekeeping and clears cache memory as needed.

Questions

• When will android clear cache in internal storage & when in removable storage?
• Will it wait for full memory or removable memory then clear it?
• Is there a specific threshold for the cache used by a particular application in internal and external memory?
• Is the cache internal and external the same, other than where are they located?